WO2007052268A2

WO2007052268A2 - Power generation by hydrothermal means

Info

Publication number: WO2007052268A2
Application number: PCT/IL2006/001260
Authority: WO
Inventors: Shmuel Tzivyon
Original assignee: Yad Konena Ltd.
Priority date: 2005-11-03
Filing date: 2006-11-01
Publication date: 2007-05-10
Also published as: WO2007052268A3; IL177522A

Abstract

A system and method for generating power using a bubble producing fluid to provide bubbles. The bubbles cause circulation of a power generating liquid within an interconnected system of tanks containing the liquid. The circulating liquid actuates a liquid turbine which is connected to a means for generating electrical energy. The system can be energized by solar radiation.

Description

POWER GENERATION BY HYDROTHERMAL MEANS

FIELD OF THE INVENTION

The present invention relates to a system and method for generating power by hydrothermal means.

BACKGROUND OF THE INVENTION

In view of global warming, alternative energy sources are at various stages of development. Perhaps the single most important non-polluting energy source being considered is solar radiation. However, up until now the cost of generating power using solar energy far exceeds that of generating electricity from fossil fuels.

Two decades ago a major power plant was built in the California desert for generating power using solar energy. It used solar radiation to generate steam which actuated gas turbines which in turn activated a generator for producing electricity. The solar radiation was collected by a bank of solar collectors through which oil was passed and heated to a temperature of 300°-400°C. The heated oil then transferred heat to a water reservoir generating steam.

The cost of building the power plant, planned to generate 80 MW, was about $280 million. The plant used a field of solar panels extending over 500000 m². This translated into a fixed cost of $3500 per kW. The plant's operational cost was about 12 cents per kW while its efficiency was about 11%.

Subsequently, another power plant was built, this time in the region of the Dead Sea, which used solar energy and operated on the same general principles as the California plant. However, instead of steam, heated Freon^® gas was used to activate the gas turbines. It was found that the heated Freon^® gas corroded the turbines in a relatively short period of time.

In view of the above, a need exists for a cheap power generating system based on solar energy. It would be desirable to develop a power generating system based on solar energy which uses relatively inexpensive components, requiring little maintenance and which can be operated at low temperatures. It would be further desirable if the system operated at temperatures which could be varied. SUMMARY OF THE PRESENT INVENTION

It is an object of the present invention to provide a low cost power generating system based on solar energy which can operate at lower temperatures than prior art power stations.

It is a further object of the present invention to provide a power generating system which can operate at any of several temperatures and incorporates a hydrothermal means for generating energy. The system should require little maintenance.

It is yet another object of the present invention to provide a method for generating energy by hydrothermal means.

There is thus provided in accordance with one aspect of the present invention a system for generating power. The system includes at least two tanks for holding a power generating liquid with the tanks connected to each other by at least a first and second conduit. The system also includes one or more liquid turbines positioned so that when the power generating liquid passes through the first conduit the liquid also passes through and actuates the one or more turbines. One or more generators are in mechanical communication with and actuated by the activated one or more turbines. The first tank has an inlet through which a bubble producing fluid is introduced. The system also includes a source for the bubble producing fluid in fluid communication with the inlet. The bubble producing fluid is delivered from the source and introduced into the first tank providing bubbles therein. The bubbles cause the power generating liquid to flow through the second conduit from the first tank into the second tank and through the first conduit into the first tank from the second tank. The power generating liquid while passing through the first conduit activates the one or more turbines which in turn actuates the one or more generators thereby generating power.

Further, in accordance with another embodiment of the system of the present invention, the source is a cooling system which cools the bubble producing fluid therein, the cooling system having a first and second end. The cooling system is in fluid communication with both of the tanks at the first end and in fluid communication with the inlet of the first tank at the second end.

In yet another embodiment of the system of the present invention, the system further includes a collector of energy through which a heat absorbing liquid flows and absorbs energy. The system also includes a heat exchanger in fluid communication with the collector of energy and through which the heat absorbing liquid flows. In this embodiment, the bubble producing fluid after flowing through a cooling system as described above passes through the heat exchanger and absorbs heat brought by the heat absorbing liquid to the heat exchanger. The heated bubble producing fluid is then delivered to the inlet of the first tank.

In a further embodiment of the system, the source includes a pump which brings the bubble producing fluid to the inlet of the first tank.

In yet another embodiment of the system, the source is a steam generating source.

In another embodiment of the system, the system further includes a means for heating the power generating liquid when the bubble producing fluid which enters the first tank is a liquefied gas. The means for heating is positioned in at least one of the tanks.

Additionally, in another aspect of the present invention there is provided a method for generating power. The method includes the steps of: introducing a bubble producing fluid into a power generating liquid in a first tank, the first tank being in liquid communication with a second tank also containing the power generating liquid; transferring power generating liquid from the first tank to the second tank via a conduit, the transferring resulting from bubbles produced by the bubble producing fluid; and conveying power generating liquid from the second tank to the first tank via a different conduit than in the step of transferring, wherein during the process of conveying the power generating liquid passes through one or more liquid turbines, the turbines connected to, and activating, one or more generators for generating power.

Additionally, in accordance with another embodiment of the method of the present invention, the method further includes the step of cooling the bubble producing fluid prior to the step of introducing. This step may further include the step of collecting heat and transferring it to the cooled bubble producing fluid prior to the step of introducing. The step of collecting heat may be effected by a solar energy collection system. In this step of cooling, the fluid may be cooled until it is liquefied.

In another embodiment of the method of the present invention, the method further includes the step of heating the power generating liquid to a temperature above the boiling point of the bubble producing fluid when the fluid is introduced as a liquefied gas and prior to its introduction. BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be understood and appreciated more fully from, the following detailed description taken in conjunction with the drawings in which:

Fig. 1 is a schematic view of a system for generating power constructed according to a first embodiment of the present invention;

Fig. 2 is a schematic view of a system for generating power constructed according to a second embodiment of the present invention; and

Fig. 3 is a schematic view of a system for generating power constructed according to a third embodiment of the present invention.

Similar elements in the Figures are numbered with similar reference numerals.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention provides a system and method for generating power by hydrothermal means at low temperatures. These temperatures may be varied as required. The system of the present invention is a hydrothermal system which may be used with a solar energy source. The system is based on using a bubble producing fluid to generate bubbles in a tank containing a power generating liquid. The bubbles reduce the specific gravity of the liquid in the tank into which the bubble producing fluid is introduced, herein called the first tank, causing the power generating liquid to flow through a connecting conduit from the first tank to a second tank. This flow causes a concomitant flow into the first tank from the second tank along another connecting conduit. The liquid flowing from the second tank to the first tank also flows through one or more liquid turbines which actuate one or more generators producing power. In addition to operating at lower temperatures then prior art conventional and solar power systems, the system uses liquid turbines which are much cheaper, have longer working lives, and require less maintenance than gas turbines.

Surprisingly, the circulation resulting from the bubbles generates power at an efficiency significantly higher than expected. The efficiency approaches 12-15%. This compares favorably with conventional polluting power stations which have efficiencies of about 22%- 25% and prior art solar power generating systems which have efficiencies of approximately 11%-12%. Reference is now made to Fig. 1 which shows a system constructed according to a first embodiment of the present invention. The system includes two tanks 1 and 2, typically, but not necessarily, metallic cylindrical tanks positioned with their long axis perpendicular to the ground, which contain a power generating liquid, typically but not necessarily water. The system includes a liquid turbine 3. Liquid turbine 3 is in mechanical communication with an electrical generator 7. Tanks 1 and 2 are in liquid communication via transfer conduit 19 and turbine actuating conduit 13. Conduit 13 leads the power generating liquid from tank 2 to and from turbine 13, emptying it into tank 1. Conduit 19 allows the power generating liquid to move from tank 1 to tank 2.

The system also includes at least one solar radiation collector, preferably a bank of solar radiation collectors 11. The solar radiation collectors contain a heat absorbing liquid, typically, but not necessarily, water, which absorbs the radiant energy collected by collectors 11. The heated liquid is brought from collectors 11 and circulated through a heat exchanger 4, the latter being in liquid communication with solar radiation collectors 11. The heat absorbing liquid is then re-pumped through the collectors by circulation pump 16.

The heat absorbing liquid flowing through collectors 11 may be water but may also be oil. These are exemplary liquids only and are not to be considered as limiting the present invention.

When water is the heat absorbing liquid, the heated water obtained from the solar collectors enters heat exchanger 4 at a temperature of typically about 55°C-60°C. However, this temperature should not be deemed to be limiting as it is a function of many factors including the number and nature of the solar collectors. Simple, commercially available solar collectors for household use such as those manufactured by Amcor Ltd. or Electra Ltd., both Israeli companies, may be used.

In heat exchanger 4, the heat absorbed by the heat absorbing liquid passing through collectors 11 is exchanged with a cooled, or even liquefied, gas arriving via entrance conduit 15, flowing through heat exchanger 4 and exiting via exit conduit 17. Typically, but without limiting the invention, the cooled or liquefied gas is a gas such as a Freon^® gas like Freon^® 141 B. If the gas is liquid when entering, it typically boils and exits the heat exchanger as a gas. The heated gas enters tank 1 via exit conduit 17 at the inlet (not numbered) of tank 1.

It should be noted that the term "gas" as used in the discussion herein is used interchangeably with the term "bubble producing fluid". The "gas" may be in its liquid or gaseous state except where specifically noted otherwise in the discussion. The gas described above is cooled, and possibly even liquefied, by a condenser 5 and further cooled by blower 8 which blows air at ambient temperature on condenser 5. It should be understood that other cooling means can be used in place of blower 8. A water (or other coolant) cooling system may also be used. Li such a case, the coolant of the cooling system circulates through condenser 5 but is itself cooled separately in a separate cooling element (not shown).

The cooled or liquefied gas flows from condenser 5 through gas tank 9 and then through a tank in fluid communication with a gas circulation pump 10. Pump 10 forces the cooled or liquefied gas through a one-way valve 20 on its way to entrance conduit 15 and heat exchanger 4. One-way valve 20 prevents heated gases exiting heat exchanger 4 from returning directly to condenser 5.

After exiting heat exchanger 4 and passing through exit conduit 17, the gas is brought to and enters tank 1. The entering gas causes strong bubbling in tank 1 and leads to a decrease in the specific gravity of the power generating liquid in tank 1. The level of the power generating liquid in tank 1 rises in relation to the level of the power generating liquid in tank 2. This causes the power generating liquid to naturally flow through transfer conduit 19 from tank 1 to tank 2 in the direction of the indicating arrows in an attempt to equalize the liquid levels in the two tanks.

It should be noted that when the gas, i.e. bubble producing fluid, enters tank 1 as a liquid, the power generating liquid must be at a temperature above the boiling point of the liquefied gas. This condition allows the liquefied gas to change phase inside tank 1 and bubble to the top of the tank as previously described. Therefore, when the gas enters tank 1 as a liquefied gas, heating elements or other heating devices may be required and these are positioned and present in tanks 1 and/or 2. These heating devices heat the power generating liquid to a temperature where it can evaporate and produce bubbles. These heating elements or devices are not shown in Figure 1. Without limiting the invention, these devices may include electrical resistors or solar heated liquids which can exchange heat with the power generating liquid in tanks 1 and 2.

When not in operation, the water level in both tanks is the same. This is a necessary consequence of turbine actuating conduit 13 connecting both tanks. Because the water in both tanks is at the same level, the pressure at the bottom of each tank is initially the same and water does not flow from one tank to the other.

The phenomenon of bubbling described above causes a decrease in specific gravity of the power generating liquid in tank 1. This decreases the pressure at the bottom of tank 1 vis-a-vis the pressure at the bottom of tank 2. Because of this pressure differential at the two ends of conduit 13, there is a steady flow of water from tank 2 to tank 1 through conduit 13 passing through turbine 3. In the Figure, arrows indicate the direction of this flow. This occurs the entire time that there is gas bubbling into tank 1. The flow caused by this pressure differential between the tanks is used to activate liquid turbine 3, typically, but without limiting the invention, a Kaplan turbine, with the activated turbine actuating generator 7, the latter producing electricity. Kaplan turbines can be obtained from many commercial sources, such as Alstom Power-Hydro Systems, Rugby, UK.

Essentially, all the gas bubbles rise to the top of tank 1 above the level of transfer conduit 19. The gas at the top of tank 1 and any residual gas that has entered tank 2, exit the tank system via gas exhaust conduits 18 and 12. The exiting gases are then brought to condenser 5 where cooling of the gas occurs as described above.

In another embodiment of the present invention, shown in Fig. 2 to which reference is now made, that portion of the system showing collectors 11 and heat exchanger 4, i.e. the solar energy providing elements, may be absent. The remaining portions of the system are identical to that shown in and discussed with Fig. 1. Identical elements of the system are numbered identically. Where the elements operate in a manner similar to that described in conjunction with Fig. 1, their operation will not be discussed again.

In Fig. 2, the cooled or liquefied gas exiting one-way valve 20 may flow directly through conduit 17 into tank 1 at its inlet. If the gas is just cooled, it enters tank 1 and bubbles to the top of the tank as described previously. If the gas enters as a liquefied gas, the power generating liquid in tank 1 is kept at a temperature above the boiling point of the liquefied gas, thereby causing the gas to evaporate. Evaporation generates bubbles which produce the same power generating liquid flows between tanks 1 and 2 as discussed above.

When the liquefied gas is introduced into tank 1, heating elements or other heating devices are required. These are present in tanks 1 and/or 2 to ensure that the power generating liquid in the tanks is at a temperature above the boiling point of the bubble producing fluid. These heating elements or other heating devices are not shown in Fig. 2.

While typically the power generating liquid in tanks 1 and 2 of the present invention will be water, this is not essential. Any power generating liquid can be used provided that no interaction, chemical or physical, between the bubble producing fluid and power generating liquid occurs. A typical, but non-limiting alternative power generating liquid may be alcohol. The density of the power generating liquid may be heavier or lighter than water. The boiling point of the power generating liquid typically is greater than that of the bubble producing fluid.

The system described herein may be an "open" or a "closed" system. A closed system as used here indicates a system where the bubble producing fluid is continuously circulating, being condensed, evaporated, and then returned to a condenser. Fig. 1 represents a closed system. What is meant by an open system here is a system where the exiting gas, originating from the bubble generating fluid, is returned to the ambient. An open system requires a constant supply of additional bubble producing fluid.

Fig. 3 to which reference is now made represents yet another embodiment of the present invention. This embodiment employs an open system.

The portion of the system shown in Fig. 1 representing the solar collectors 11, the heat exchanger 4, and the circulation pump 16 are absent. Similarly the entire cooling system, elements 5, 8, 9 10, 20 and 15 of Fig. 1 are absent. Present is element 32 which represents a steam generator which provides steam via conduit 17 to the inlet (not numbered) of tank 1. Upon entering tank 1 the steam bubbles to the surface of tank 1 and exits directly to the ambient. Conduits 12 and 18 of Fig. 1 are absent as they are not required in an open system such as Fig. 3. The power generating liquid circulates as in Fig. 1 through conduits 13 and 19 in the direction indicated by the arrows. Turbine 3 produces power as a result of liquid flowing through conduit 13.

In other embodiments more than a single liquid turbine may be used with the system of the present invention. When more than a single liquid turbine is used, the turbines may be positioned on the same turbine actuating conduit or each turbine may be positioned on a different turbine actuating conduit.

In yet other embodiments of the present invention more than two tanks may be present in the system.

When a closed system constructed according to the present invention is used, the temperature differential between the bubble producing fluid and the power generating liquid in tanks 1 and 2 determines the amount of power generated. For a closed system as in Fig. 2, the determining temperature differential is the temperature of the power generating liquid in tanks 1 and 2 less the temperature of the bubble producing fluid in condenser 5. For the closed system in Fig. 1, the determining temperature differential is the temperature of bubble producing fluid as it leaves heat exchanger 4 less the temperature of the bubble producing fluid at condenser 5. For an open system, the temperature differential is essentially irrelevant in determining the amount of power generated.

In general, the larger the temperature differential the greater the flow of the liquid and the greater the electric power generated. The temperature differential that can be used with systems constructed according to the present invention may range between about slightly above 0° to 250 ⁰C.

The present invention is not necessarily intended to operate at a single fixed temperature as with other power generating systems. Operating temperatures may be varied. However, the system described herein is typically operated at temperatures much lower than other power generating systems.

In a prototype system using the embodiment shown in Fig. 2, Freon^® 141 B was used as the circulating gas, i.e. as the bubble producing fluid, and water as the power generating liquid in tanks 1 and 2. The water (bubble producing fluid) in condenser 5 was kept at a temperature of 2O⁰C and the water (power generating liquid) in tanks 1 and 2 was kept at a temperature of 6O⁰C. The tanks where heated by resistive heating elements and the temperature controlled by a thermostat. The efficiency of the system was found to be about 15%.

It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described herein above. Rather the scope of the invention is defined by the claims that follow:

Claims

What is claimed is:

1. A system for generating power, said system comprising: at least two tanks for holding a power generating liquid, said tanks connected to each other by at least a first and second conduit; at least one liquid turbine positioned so that when the power generating liquid passes through said first conduit the liquid also passes through and actuates said turbine; at least one generator in mechanical communication with and actuated by said at least one turbine; an inlet in said first tank through which a bubble producing fluid is introduced; and a source for the bubble producing fluid, said source in fluid communication with said inlet, wherein the bubble producing fluid is delivered from said source and introduced into said first tank providing bubbles therein, the bubbles causing the power generating liquid to flow through said second conduit from said first tank into said second tank and through said first conduit into said first tank from said second tank, the power generating liquid while passing through said first conduit activating said at least one turbine which in turn actuates said at least one generator thereby generating power.

2. A system as in claim 1 wherein said source is a cooling system which cools the bubble producing fluid therein, said cooling system having a first and second end, the cooling system in fluid communication with both of said tanks at said first end and in fluid communication with said inlet at said second end.

3. A system as in claim 2 further including: a collector of energy through which a heat absorbing liquid flows and absorbs energy; and a heat exchanger in fluid communication with said collector of energy and through which the heat absorbing liquid flows, and wherein the bubble producing fluid after flowing through said cooling system passes through said heat exchanger and absorbs heat brought by the heat absorbing liquid to said heat exchanger, the heated bubble producing fluid then being delivered to said inlet.

4. A system as in claim 1 wherein said source further includes a pump to bring said bubble producing fluid to said inlet.

5. A system as in claim 1 wherein said source is a steam generating source.

6. A system as in claim 1 further including a means for heating the power generating liquid when the bubble producing fluid which enters said first tank is a liquefied gas, said means for heating positioned in at least one of said tanks.

7. A method for generating power, said method comprised of the following steps: introducing a bubble producing fluid into a power generating liquid in a first tank, the first tank being in liquid communication with a second tank also containing the power generating liquid; transferring power generating liquid from the first tank to the second tank via a conduit, the transferring resulting from bubbles produced by the bubble producing fluid; and conveying power generating liquid from the second tank to the first tank via a different conduit than in said step of transferring, wherein during said conveying the power generating liquid passes through at least one liquid turbine connected to and activating at least one generator for generating power.

8. A method according to claim 7 further including the step of cooling the bubble producing fluid prior to the step of introducing.

9. A method according to claim 8 wherein the bubble producing fluid is cooled until it is liquefied.

10. A method according to claim 8 further including the step of collecting heat and transferring it to the cooled bubble producing fluid prior to said step of introducing.

11. A method according to claim 10 wherein said step of collecting heat is effected by a solar energy collection system.

12. A method according to claim 7 further including the step of heating the power generating liquid to a temperature above the boiling point of the bubble producing fluid when the fluid is introduced as a liquefied gas.